Distribution: N - Frl (TSB 35606), Ven (Nimis 1994), TAA (Nascimbene 2005), Piem (TSB 34783).
Description: Thallus crustose, mostly endosubstratic, rarely very thinly episubstratic, usually continuous, rarely finely areolate, mostly pale blue-green, sometimes white to yellowish-ochre (mainly in the epilithic forms). Medulla white, I- (rarely I+ pale blue). Apothecia lecideine, adnate and constricted at base, black, epruinose and somehow shiny or finely bluish-pruinose, 0.2-1.5(-2.5) mm across, with a distincly umbonate disc and a thick, prominent, doubled proper margin, resembling those of Umbilicaria crustulosa. Proper exciple black, the hyphae 5-9 µm thick, K- or K+ reddish brown; epithecium blue-green or greenish brown (the two colours often present in the same apothecium); hymenium colourless or greenish in upper part, 70-130 µm high; paraphyses coherent, branched and anastomosing, 1.7-2.2 µm thick at mid-level, the apical cell to 3 µm wide; hypothecium green- to brown-black, the upper part more intensive green, K- or K+reddish brown, c. as high as the hymenium. Asci 8-spored, clavate, with a I+ pale blue tholus and a central amyloid tube, approaching the Porpidia-type. Ascospores 1-celled, hyaline, ellipsoid, 11-28(-30) x 6-13(-18) µm, halonate, the perispore to 3 µm thick. Pycnidia black, immersed, globose. Conidia bacilliform, 3.5-9 µm long. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: on exposed calcareous rocks near and above treeline, often associated with Hymenelia coerulea; probably more widespread in the Alps.